Test 1 Flashcards
Where does the digestion of carbs begin?
In the mouth, saliva is added to the food and the enzymes within it start breaking it down
Where is saliva sourced from?
Parotid, sublingual (under the tongue), and submandibular glands
What is saliva composed of?
- mostly water derived from extracellular fluids
- alpha amylase/salivary amylase
- mucoid proteins
- bicarbonates
- electrolytes
- lysosomes
What is the purpose of lysosomes in the saliva?
Enzymes that break down protein and bacteria
What is the purpose of mucoid proteins in saliva?
Gives saliva its viscous quality, helps lubricate the food, makes it easier to swallow
What happens to carbs when you chew? What effect do we see when this is prolonged, with a cracker for example?
- chewing mixes saliva with food and increases contact area so that salivary amylase can start to breakdown glucose chains within starches
- PROLONGED CHEWING = taste sweeter because some starch will break down into disaccharide sugars like maltose which tastes sweeter than starch
What first happens when the carbs are emptied from the stomach to duodenum?
Acid is neutralized by sodium bicarbonate from the pancreas, digestion proceeds fairly quickly
The next step in the duodenum involves the addition of alpha amylase, what is this secreted by?
Secreted by the pancreas
Describe the function of the additional alpha amylase in the duodenum
- continues to hydrolyze/break down the starches into small glucose polymers and maltose
- the hydrolysis of almost all starches to maltose is almost complete when the breakdown/chyme will enter into the illum
What is the third step in the duodenum?
- the disaccharides and polysaccharides are further digested by specific enzymes that are located within the brush border of intestinal cells (as soon as the disaccharides come in contact with the brush border, they are digested by the enzymes (lactase, sucrase, maltase)
What does lactase help break down?
Lactose > glucose and galactose
What does sucrase help break down?
Sucrose>glucose and fructose
What does maltase help break down?
Maltose>2 glucose molecules
The major monosaccharides that result from the digestion of polysaccharides and disaccharides are _
glucose, fructose, galactose
What are the major monosaccharides absorbed via?
Carrier mediated transport processes
The transporters that actually help mediate/help with the uptake of monosaccharides in the epithelial cell are _
sodium monosaccharide co-transporters
What are the most common transporters of monosaccharides?
Sglt1 (sodium dependent glucose transporter) and GLUT-5 (a sodium independent facilitated diffusion transporter with a specificity for fructose)
For each molecule of glucose, _ are transported into _ via the co-transporter
2 sodium ions, epithelial cell
What is the only other carb that uses sglt1 in the same way as glucose?
Galactose
What transports sodium back into the gut lumen
Sodium potassium ATPase pump
What happens to monosaccharides when they enter the enterocyte?
- a separate monosaccharide transporter on the contra-luminal side of the epithelial cell will accept all three of the monosaccharides (GLUT 2)
- the monosaccharides then enter the circulation to reach the hepatic portal vein which transports them to the liver
What happens to transporters when we increase our amount of dietary carbohydrate intake?
The number and activity of these transporters isn’t static and may respond to nutrient uptake
- increased in sglt1 can be observed after increasing amount of dietary carbohydrate intake
** The REVERSE is also true
What happens to transporters when we reduce dietary carbohydrate intake?
This will down regulate the transporters and reduce the absorptive capacity for each carb (there are 12 glucose transporters named glut 1-12 and all will use facilitated diffusion in order to transport the monosaccharides)
The different glucose transporters have different functions and _
Are expressed at different levels of different tissues (ex. GLUT 4 in muscle)
Protein digestion will breakdown ingested proteins into _
Simple amino acids, dipeptides and tripeptides
The process called hydrolysis happens where? What is it dependent on?
- takes place in the stomach and small intestines (intestinal mucosa)
- depends on very specific protein digesting enzymes known as proteases as well as the acidity of the stomach
What PH level can we expect in the stomach?
So acidic that the pH in the stomach and the gastric contents typically sit around 2.0
What is pepsin and where does it come from?
- an important group of proteases
- will be secreted originally as a precursor (pepsinogen) from the cells of the stomach wall
- will be initially inactive but as soon as pepsinogen contacts the hydrochloric acid within the stomach it’s immediately converted into the active pepsin that will break down the protein
What is pepsin’s role in digestion?
- will degrade some of the collagenous connective tissue fibers around meat and after dismantling these fibers, other proteases can digest the remaining animal protein
What percent of ingested proteins will stomach enzymes and acids break down?
10-20% (will attack some of the longer and more complex protein strands)
What effect does the pH in the stomach cause on proteins?
The low peach in the stomach will cause denaturing of the proteins
- the 3D structure of the protein and coils and is broken down into smaller polypeptide/peptide units
What happens to pepsin when the chyme passes into the small intestine?
Becomes inactivated due to the relatively high pH in the duodenum
What is trypsin, where does it come from, and what does it do?
Protease
- released from the pancreas
- will become active to digest some of the remaining proteins and polypeptides
Pancreatic juice is rich in what?
Very rich in the precursors for all sorts of proteases, which will help digest polypeptides into tripeptides, dipeptides, and single amino acids
- ultimately can be transported across some of the enterocytes
At the absorption stage of proteins, we’ve broken everything down into _?
Amino acids, dipeptides or tripeptides
Amino acids, dipeptides and tripeptides can be absorbed through _. Describe the absorption process
Active transport
- usually coupled to transport of sodium within the small intestine, ultimately will be delivered to the liver via the hepatic portal vein
- any dipeptides or tripeptides that have been transported across the endothelial membrane will be broken down inside of the cell into their amino acid constituents by specific dipeptidases and tripeptidases
The majority of amino acids will be transported across the epithelium against _. Therefore we need _
Concentration gradient, need carrier mediated transport
Aside from transport proteins, we also have
Brush border enzymes
How long are short chain fatty acids? What about large chain fatty acids?
10-12 carbons, more than 10-12 carbons
Describe how short chain fatty acids are absorbed
- short chain fatty acids can just diffuse through the brush border since our cell membranes are made of phospholipids
- from there they can diffuse through the basolateral surface and ultimately be taken up by the capillaries along with the amino acids/monosaccharides
Larger fatty droplets or structures need to be broken down via a process called _. What does this rely on?
Emulsification
- realize on bile salts to transform the large lipid droplets into much smaller ones
Describe the function of bile salts
- bile salts mix with lipids and act as a detergent in order to disrupt those lipid droplets and therefore decrease the droplet size
- this in turn will increase the surface area of the lipid exposed to various lipases/digestive enzymes/transporters and they can continue to move along
When bile salts surround large chain fatty acids we get _
Micelles
What is the function of micelles
Facilitate the movement of larger fatty acid chains directly to the brush border
- drops contents off and the fatty acid chain can be brought into the cell via simple diffusion
- this allows them to pass through and reform as triglycerides
Reform triglycerides are packaged into _
Chylomicrons (large molecules surrounded by a protein coat)
What happens to chylomicrons after they are formed?
- chylomicrons can’t be taken up in the capillary and instead are exocytosed to the lacteals present in the lamina propria
- eventually the fat will be carried to a larger vessel (thoracic duct) together, monosaccharides, amino acids, and small short chain fatty acids can be taken up into the blood
- however anything that must initially be contained within a chylomicron will be taken up initially by the lacteal and eventually return to the blood in larger veins
Describe the thoracic duct
The thoracic duct is a part of the lymphatic system and connects to the cardiovascular system at a junction where the left internal jugular vein will come in contact with the left subclavian vein
Where do the absorbed nutrients go?
- they’re gathered up in the villa and transported to the liver via blood flow, ultimately leading to the hepatic portal vein
- liver will filter them before sending off the fuel to the rest of the body
- the lacteals will send the chylomicrons to the larger lymphatic vessels, ultimately to the thoracic duct
- this connects to venous system at left subclavian vein (fat rejoins circulation)
= Pumped into heart + around body = absorbed nutrients
